Various Computer Assisted Orthopedic Systems (CAOS) tools exist, which range from active robotic to passive or navigation systems. Active robotic systems are capable of performing surgery autonomously without interaction of the surgeon. Many times, the surgeon wants to be in control of the surgery, wherein the passive or navigation systems are preferred, which provide additional information during a procedure compared to conventional surgery but do not perform the surgical action. The surgeon controls the intervention but acts on additional patient information obtained from a pre-operative scan.
For an orthopedic intervention using a CAOS system, a pre-operative plan may or may not precede the actual surgery. One such system is the development of a surgical template, also referred to as a surgical guide, to be used during surgery to guide the surgical tools. The pre-operative plan may aid the surgeon to take decisions about the surgery before it commences. The pre-operative plan may be based on a three-dimensional scan of the patient, such as a CT or MRI scan. During planning, the surgeon will have access to the internal structures of the patient to plan the surgery, for example by volumetric scan data that can be displayed slice by slice, from various angles, etc. Planned paths of instruments relative to patient data are transferred to the surgical template. During surgery, the surgical template guides the path of the instrument. Hence, the system offers little flexibility for the surgeon to deviate from the planned path should that be necessary during the surgery. However, this is one way of physically integrating the pre-operative plan with the actual surgery. A benefit of the system is that the physical components do not need to be calibrated before surgery commences.
Robotic surgery is another possibility to carry out a pre-operatively plan. During the surgery, the surgical instrument is not in the hands of the surgeon but carried by a robot, which is only indirectly controlled by the surgeon. Since the physical components such as a camera and a robotic arm, are provided as an integrated unit, calibration between the components is not necessary. Therefore, these systems are not only costly, but their flexibility is limited by the degrees of freedom and limited feedback to the surgeon to take corrective actions.
Common to robotic surgical systems is that they use a navigation system to guide the robot. Such navigation systems can comprise three major components: the surgical aspect, the virtual aspect, and the navigator. The surgical aspect is the bones and accompanying tissues in the surgical field. The virtual aspect is the virtual representation of the surgical aspect. Finally, the navigator establishes a coordinate system in which the location and orientation of the target as well as “end-effectors” are expressed. The “end-effectors” can be surgical instruments or active devices used during surgery.
Three major procedural requirements are essential to successful navigation. First, end-effectors must be calibrated for correct representation of their shapes and geometry in the coordinate system established by the navigator. Second, “registration” establishes correspondence between the surgical and the virtual aspect. Finally, “dynamic referencing” using dynamic reference bases establishes a local coordinate system that compensates for possible motion of the navigator or the surgical aspect during surgical action.
Examples of robotic surgical systems are the RoboDoc surgical system, the Acrobot system, and the CASPAR system. Common to them is that they use pre-operative and intraoperative data obtained through computer navigation to control the performance of the robot. In these systems, the surgical aspect is registered in the coordinate system of the robot to provide correspondence between the virtual and the surgical aspect, and the actions of the robot is controlled by the virtually planned path or movements of virtual end-effectors. The position of the robotic arm is known in its coordinate system. This makes it possible to also have a fixed relationship between the coordinate system of the robot and the coordinate system of the plan for the surgery, and further calibration is not required.
Patient anatomical landmarks can be identified by cameras while the patient is positioned within reach of the robotic arm. In the pre-operative plan, the same anatomical landmarks are present. The pre-operative plan contains planned movement of end-effectors relative the anatomical landmarks. During surgery, the same anatomical landmarks are identified and movement of the robot can be controlled in relation thereto based on the plan data to position orthopedic implants. The surgery is restricted by the operating range of the robot. The pre-operative plan may be implemented by the robot, whereby the end-effectors are completely controlled by the plan data, such as in the RoboDoc system. Alternatively, the plan data can be used to apply active constraints, as in the Acrobot system, such that the surgeon is assisted to achieve accurate cuts and paths while ensuring the pre-operative plan is followed. Common to these systems is that the surgeon is more or less restricted by the robotic system, and is not fully free to make his own choices during surgery.
Attempts to use Stereotactic surgery for surgical interventions have ben made. However, the difficulty to obtain a reliable bone reference has limited this type of surgery to brain surgery. Before scanning the patient, a frame is attached to the scull of the patient. The frame is used as a fiduciary marker to register the patient to the scan data during the surgery, and to track the position of a surgical instrument to the reference frame, and, thus, to the patient data. During the surgery, the tip of a probe can be tracked and related to the patient scan data. However, systems using artificial landmarks that are present during scanning, such as CT and/or MRI scanning, as well as during surgery for registering patient scan data to patient data are not useful for orthopedic surgery. An example of such as system is for example described in WO 96/11624. During the surgery, these systems relate patient scan or segmented data, such as in the form a 3D representation of the scan data, to the tracked position of the surgical instrument to provide additional information to the surgeon, such as intraoperative measurement tool and tracking of tools with respect to bony anatomy displayed on the screen, and act on information in a timely manner. However, the purpose of these systems is to provide information about anatomical structures that otherwise would not be visible to the surgeon, but do not give any guidance. Recently, attempts have been made to rely on anatomical landmarks rather than artificial landmarks for the registration of the patient's image data set to the position of the instrument. However, these systems are still limited to displaying the patient image data relative to the position of the surgical instrument. Also, the data displayed are intrinsic to the patient scan data, and do not relate to the planning of an implant.
Orthopaedic surgery MIS (Minimally Invasive Surgery) procedures have been proposed for the planning of orthopedic implant surgeries. Such systems do not rely on volumetric patient image data. Instead, these systems are image free and use information gathered intra-operatively—such as centers of rotation of the hip, knee, and ankle and visual information like anatomical landmarks—from which desired positions of the implants are calculated. These systems provide no planning capabilities before the surgery and navigation is based on the information that is calculated rather than obtained from the patient's true anatomy. Structures shown on a screen are always approximations, such as 3D models obtained from a library of bones structures based on the calculations made. Hence, such are less precise compared to image based orthopedic navigation systems. Furthermore, these systems do not provide any pre-operative planning possibilities, since the calculations and simulations are made intra-operatively. Furthermore, surgical tools are not tracked during the surgical action. Such system is for example disclosed in US application No. 2011/0275957.
WO 2011134083 discloses systems and methods for surgical guidance and image registration, in which three-dimensional image data associated with an object or patient, is registered to topological image data obtained using a surface topology imaging device. The surface topology imaging device may include fiducial markers, which may be tracked by an optical position measurement system that also tracks fiducial markers on a movable instrument. The instrument may be registered to the topological image data, such that the topological image data and the movable instrument are registered to the three-dimensional image data. The system may also co-register images pertaining to a surgical plan with the three-dimensional image data. The fiducial markers may be tracked according to surface texture. The system utilizes fiducial markers attached to surgical instruments that have a fixed relationship relative to an end-effector thereof. Hence, the system becomes complicated and expensive, since special-purpose surgical instruments having the fiducial markers have to be used with the system. The position of the end-effector of the surgical tool is determined and recorded using a 3D model of the surgical tool, which is imported from computer aided design (CAD) drawings, in which the tool tip is known. Alternatively, the surgical tool can be profiled with a structured light scanner to obtain its 3D geometry. The tool tip and orientation axis are determined from an acquired point cloud. These are time-consuming processes for obtaining the positions of the tool tip relative the fiducial markers, which is undesired during surgical action where time is a scarce resource, not only during the surgical action itself but also in preparation therefore. US2009234217A1, US2011251607, and US2007238981A1 disclose various aspects of navigation systems. However, utilizing various types of fiducial markers, they all suffer from at least the same issues as the navigation system disclosed in WO 2011134083, such as in relation to the calibration of the position of the end-effector or tool-tip.
Hence, an improved surgical navigation method and system and associated surgical instruments would be advantageous, and in particular allowing for improved guidance, precision, increased flexibility, cost-effectiveness, robustness, reliability, efficiency and/or patient safety would be advantageous.